An important component of the fire extinguishing system – Check Valve (Part 2)

Jun 2, 2023 | news

Performance parameters of check valve

Body material		Nominal pressure (MPa)	Operating temperature (℃)	Applicable medium
Carbon steel		1.6-6.4	≤425	Water, oil, steam
Carbon steel		10.0-16.0	≤450	Water, oil, steam
Stainless steel	P	1.6-16.0	≤200	Nitric acid
Stainless steel	R	1.6-16.0	≤200	Acetic acid
Chromium-nickel-titanium steel	PI	1.6-6.4	≤550	Petroleum, Petroleum Products
Chrome-molybdenum steel		1.6-16.0	≤550	Oil

Nominal pressure	Nominal diameter	Main connection size									Overall dimension
PN	DN	L	D	D1	D2	D6	b	f	f1	Z-φd	H
1.6MPa	40	200	145	110	85	–	16	2	–	4-18	95
	50	230	160	125	100	–	16	2	–	4-18	105
	65	290	180	140	120	–	18	2	–	4-18	120
	80	310	195	165	135	–	20	3	–	8-18	130
	100	350	215	180	155	–	20	3	–	8-18	140
	125	400	245	210	185	–	22	3	–	8-12	155
	150	480	280	240	210	–	24	3	–	8-23	180
	200	600	335	295	265	–	26	3	–	12-23	215

Check valve selection standard

In order to prevent the reverse flow of the medium, check valves should be installed on the equipment, devices, and pipelines;
Check valves are generally suitable for clean media, and should not be used for media containing solid particles and high viscosity;
Generally, horizontal lift check valves should be used on horizontal pipes with a nominal diameter of 50mm;
Straight-through lift check valves can only be installed in horizontal pipelines;
For the inlet pipeline of the pump, the bottom valve should be selected. The bottom valve is generally only installed on the vertical pipeline of the pump inlet, and the medium flows from bottom to top;
Compared with the swing type, the lifting type has better sealing performance and greater fluid resistance. The horizontal type should be installed on horizontal pipes, and the vertical type should be installed on vertical pipes;
The installation position of the swing check valve is not limited. It can be installed on a horizontal, vertical, or inclined pipeline. If it is installed on a vertical pipeline, the flow direction of the medium should be from bottom to top;
The swing check valve should not be made into a small-diameter valve. It can be made into a very high working pressure. The nominal pressure can reach 42MPa, and the nominal diameter can also be made very large, the maximum can reach more than 2000mm. Depending on the material of the shell and the seal, it can be applied to any working medium and any working temperature range. The medium is water, steam, gas, corrosive medium, oil, medicine, etc. The working temperature range of the medium is between -196–800°C;
The swing check valve is suitable for low pressure and large diameter, and the installation occasion is limited;
The installation position of the butterfly check valve is not limited, it can be installed on the horizontal pipeline, or the vertical or inclined pipeline;
Diaphragm check valves are suitable for pipelines that are prone to water hammer. The diaphragm can well eliminate the water hammer caused by the reverse flow of the medium. It is generally used on low-pressure and normal-temperature pipelines, especially for tap water pipelines. The temperature is between -12–120°C, and the working pressure is <1.6MPa, but the diaphragm check valve can be made with a larger diameter, and the maximum DN can reach more than 2000mm;
Ball check valves are suitable for medium and low-pressure pipelines and can be made into large diameters;
The shell material of the ball check valve can be made of stainless steel, and the hollow sphere of the seal can be wrapped with polytetrafluoroethylene engineering plastics, so it can also be applied to the pipeline of general corrosive media, and the working temperature is -101–150 ℃, the nominal pressure is ≤4.0MPa, and the nominal flow range is between DN200—DN1200;
When selecting a check valve for incompressible fluids, the required closing speed must first be evaluated, and the second step is to select the type of check valve that may meet the required closing speed;
The check valve for compressible fluid can be selected according to a similar method of check valve for incompressible fluid. If the medium flow range is large, the check valve for compressible fluid can be used as a reduction device, if the medium flow is stopped and started rapidly in succession, as in the outlet of a compressor, a lift check valve is used;
The corresponding size of the check valve should be determined, and the valve supplier must provide the data of the selected size so that the valve size can be found when the valve is fully open at a given flow rate;
For high and medium pressure check valves below DN50mm, vertical lifting check valves and straight-through lifting check valves should be selected;
For low-pressure check valves below DN50mm, butterfly check valves, vertical lift check valves, and diaphragm check valves should be used;
For high and medium pressure check valves with DN greater than 50mm and less than 600mm, swing check valves should be selected;
For medium and low-pressure check valves with DN greater than 200mm and less than 1200mm, it is advisable to choose a wear-free spherical check valve;
For low-pressure check valves with DN greater than 50mm and less than 2000mm, butterfly check valves and diaphragm check valves should be selected;
For pipelines that require relatively little water hammer or no water hammer when closing, slow-closing swing check valves and slow-closing butterfly check valves should be selected.

Check valve common troubleshooting

Disc broken

The cause of the disc breaking is

The pressure of the medium before and after the check valve is in a state of close balance and “seeing” with each other. The valve disc often beats with the valve seat, and the valve disc made of some brittle materials (such as cast iron, brass, etc.) is broken.

The preventive method is to use a check valve with a tough material as the disc.